The invention concerns a hydraulic machine, in particular a steering aid pump and particularly relates to the positioning of the drive shaft and elements on the shaft.
Hydraulic machines of the type described here are well-known. They are characterised by a drive shaft, to the first end of which is attached a drive wheel, also described as a swash plate, via which a torque is introduced to the drive shaft by means of a specially designed belt. This serves to drive a pump unit which is located at the other end of the drive shaft and which is comprised of a first rotating (pump) element driven by the drive shaft and a second fixed (pump) element. This works in conjunction with the first (pump) element. There is a bearing unit between the two ends of the drive shaft.
Above the drive wheel is a belt, the tensile force of which is characterised by a force element which is directed radially to the center axis of the drive shaft and which bend the shaft and move them from their initial position. In hydraulic machines and steering aid pumps of the type described here, belt tensile forces are effective in such a way that there is a tangible deflection of the end of the shaft attached to the drive wheel, and thus of the drive shaft. The opposite end of the shaft, which is attached to the first, rotating (pump) element is deflected in the opposite direction, because of the bearing unit between the two ends of the shaft. Thus the first, rotating (pump) element is positioned inside the second, fixed (pump) element, which leads to increasing vibration, and therefore to persistent noises, but also leads to increased wear. The noises can be caused by the vibration, and by the fact that the two (pump) elements come into direct contact with one another when the machine is running.
A pump is known from German publication DE 34 39 311 A1, in which the middle section between the rotating and the fixed pump element, which is brought forward by the belt tension on the shaft, is balanced out by the fact that the fixed pump element, which is also called the lifting ring, shifts position. This means that the positioning of the rotating pump element can be adjusted to compensate in relation to the lifting ring. However the rotating pump element, also called the rotor, takes up a position adjusted in relation to the pressure plate. This means that noises are generated when the pump is operating, as the control or pressure ducts found in the pressure plate or the lid overscore the joints in the pump either too early or too late. This disrupts the `timing` of the pump. Furthermore, there is the disadvantage that when the lifting ring shifts, the hydraulic connections running with it are also shifted, so that they are no longer flush with the control or pressure ducts. This means that there are edges, which cause a significant amount of noise when the pump is operating.